Processes of ecosystems that contribute to human welfare often are called "ecosystem services." Daily (1997) lists the following:

purification of air and water

mitigation of floods and droughts

detoxification and decomposition of wastes

generation and renewal of soil and fertility

pollination of crops and natural vegetation

control of the vast majority of potential agricultural pests

dispersal of seeds and translocation of nutrients

sources of crop varieties, medicines and industrial enterprise

protection from the sun's harmful ultraviolet rays

partial stabilization of climate

moderation of temperature extremes and the force of wind and waves

support of diverse human cultures

provision of aesthetic beauty and intellectual stimulation that lift the human spirit

Today, a decade after the list above was compiled, we would add the storage (or 'sequestration') of atmospheric carbon to this list of important ecosystem services. Scientists generally now believe that we have entered a period of climate change caused by elevated levels of carbon dioxide and some other gases in the atmosphere. Ecosystem processes remove carbon dioxide from the atmosphere, return the oxygen into the air and incorporate the removed carbon into biomass (biological materials, such as wood).

The existence of these services often is taken for granted. However, expansion of the human population and resulting losses of many natural areas have led to widespread reductions in ecosystem services.

The Millennium Ecosystem Assessment (MA) examined global trends in ecosystem services. This study began in 2001 and was conducted under the auspices of the United Nations. The MA found that human activities have caused declines in twenty of twenty-four services examined. In addition, degradation of ecosystems services could grow significantly worse during the first half of this century.

Local reductions in ecosystem services are known. In Virginia, declines in wild pollinator populations have led owners of some fruit orchards to hire beekeepers to place colonies of honey bees in the orchards at critical times, to assure pollination of their fruit trees. Forests cover promotes clean water and biological health of streams. A 2006 study in the Rivanna River basin by StreamWatch found a negative relationship between the densities of the human populations in stream watersheds and assessed biological health of the streams.

Clearly, sustained existence of human communities depends on existence of ecosystem services. Further, we know now that we cannot assume that remaining natural systems will provide sufficient quantities of services we need. One concern is the fact that landowners who maintain forests or other natural areas on their property typically receive no economic return for the ecosystem services their natural systems provide. However, developing those properties in ways that damage or eliminate ecosystem services can produce large financial returns.

Some scientists now are working to develop methods for economically valuing ecosystem services provided by particular natural areas. For example, Everette Kline of the Virginia Department of Forestry and various colleagues have been developing tools to estimate ecosystem services generated by forests, on a parcel by parcel basis.

One goal of these efforts is creation of systems that provide economic compensation to landowners who preserve natural systems on their properties. However, attaching dollar values to ecosystem services has proven challenging, in part because ecosystem services generally have not been bought and sold. One early, well known exploration of the economic value of ecosystem services (Costanza et al 1997) estimated the value of global ecosystem services at US $ 33 trillion per year, more than the value of gross national products of all nations at that time.

Sound land use planning should aim to provide sufficient ecosystem services. Recently, Albemarle County, the City of Charlottesville and Advocates for a Sustainable Albemarle Population (ASAP) agreed to conduct a study of the local human ecological carrying capacity. In part, this study aims to identify the number of people that can exist in our community within the limits of ecosystem services generated in local open spaces.